The present invention relates to a valve actuated shunt, drain, or infusion system for fluids in the living body for which the control of the fluid flow in the system is determined by the difference between the pressure of the fluid and the pressure in a bodily region external to the shunt tubing. As a specific example, this is applied to a hydrocephalus shunt valve system in which the differential pressure control is between the ventricular fluid pressure and the pressure in the surrounding brain or the pressure which is at the surface of the brain.
Usually shunt valves for treating hydrocephalus involve an in-line serial valve which allows a predetermined flow rate as a function of the difference between ventricular and venous pressure. This is simply done by inserting in-line with the shunt tubing a valve with a certain pressure-flow characteristic between its inlet and outflow tubes. An alternative servo-valve scheme has been proposed by Hakim, U.S. Pat. Nos. 4,106,510, 3,886,948, and 3,924,635, which seeks to regulate the pressure-flow characteristic of such an in-line valve system as a function of the difference between the sub-dural stress on the brain, and the venous pressure. The basis for the Hakim designs is the hypothesis that there is a pressure gradient across the brain, and that to treat hydrocephalus one should maintain the sub-dural stress at zero relative to the venous pressure.
The present invention involves a different means of regulation of the fluid flow in such a fluid shunt system. An illustration of the invention would be a valve in a shunt system which is opened, or perhaps closed, by the relative difference between the fluid pressure in the system at the source side of the flow at the location of the valve and the pressure in some bodily region different from either the fluid source or fluid sink region, i.e. input and outflow regions, respectively. A specific example is used as an illustration involving a hydrocephalus shunt system in which an indwelling valve is opened when the source fluid pressure in the ventricles of the brain become larger, by some prescribed amount, than the pressure at the surface of the brain. This could then maintain, for example, the difference between the ventricular fluid pressure and the pressure at the surface of the brain to be zero or some prescribed value. Thus, such a design differs in concept and objectives from either previous standard shunt designs or the Hakim servo-valve design. We shall often refer to the present invention as a sensor-valve.